The invention generally relates to optical recording and storage drives, and more particularly, to a system and a method for calibrating the proper output power of a light emitting device.
As requirements for high volume storage mediums continue to increase, compact disks (CDs) are playing a more important role. During the recording process, pits are created on the CD by an optical pickup unit (OPU) of the CD recorder when by emitting a light beam on a dye layer. Lands are formed on the CD when no light beam is emitted thereon. Pits have a lower reflectivity than the lands, and pits and lands represent the information of 0 and 1.
However, pits produced by laser beams of different output power levels from different CD recorders are usually shaped differently, which causes difficulty in the process of reproducing the recorded information. This is a result of the variation in the assembly of the OPU and inconsistencies in the photo diode properties. Therefore, the CD recorder has to have its laser power calibrated prior to the fab-out stage so that the OPU can provide laser beams of the correct power.
FIG. 1 shows a power calibration system 100 as disclosed by Liu, et al. in published U.S. Patent Application No. 2003/0208332A1. Referring to FIG. 1, the power calibration system 100 is used for calibrating a laser diode 102, wherein the laser diode 102 is positioned within an optical recording drive 104. The optical recording drive 104 comprises a CD plate 106, which can move in and out of the optical recording drive 104. During calibration, a first module 108 is positioned upon the laser diode 102 in order to receive the laser beam from laser diode 102. The second module 110 is coupled to the first module 108 and a computer 112, and the computer 112 is coupled to the first module 108 and the optical recording drive 104.
Although not shown, in addition to requiring control to be performed by the computer 112, the power calibration system 100 requires the application of a standard photo diode to be used with the power calibration system. These requirements significantly increase the manufacturing costs. Additionally, in order to command the laser diode 102 of the optical recording drive 104 to progressively emit light beams of increasing power levels, the optical recording drive 104 must be equipped with some kind of a digital port to receive commands from the computer 112. For computer based peripherals, an ATAPI interface is typically used for this purpose. However, in order to reduce costs, stand-alone consumer electronic DVD recorders are not equipped with ATAPI interfaces because they are not needed during normal operations. Therefore a light emitting device calibration method for the laser diode of DVD recorders and other products having light emitting devices is required.